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Timing might be everything when it comes to treating Alzheimer's disease, according to research being presented Monday at a meeting of the American Neurological Association in Boston.

There is no cure for the mind-wasting disease that affects more than 5 million people in the USA, and numbers are expected to triple by 2050 as the Baby Boomers age. The government announced a bold plan in May to find a way to prevent the most common form of dementia by 2025. The annual cost of care for patients with Alzheimer's is estimated at more than $172 billion, says the New England Journal of Medicine, and will increase to a trillion dollars by 2050 unless "disease-modifying treatments are developed."

Researchers on Monday will discuss additional findings on two large drug trials. Results announced last summer found the treatments failed to improve either cognition or daily functioning compared with a placebo. The bapineuzumab and solanezumab therapies were done on patients with mild to moderate forms of the dementia. The drugs target beta amyloid, a toxic protein in the brain believed to cause the disease.

"We think we've been starting trials too late in the progression of the disease,'' says Laurie Ryan, director of Alzheimer's disease clinical trials at the National Institute on Aging.

Scientists are discovering mechanisms of the diseases and how it progresses. A large study published Aug. 30 in the New England Journal of Medicine found changes in the brain begin as early as 25 years before the onset of symptoms.

"I'm worried that we're intervening too late and that we're intervening with too little (of the trial drugs),'' says Reisa Sperling, director of the Center for Alzheimer's Research and Treatment at Brigham and Women's Hospital in Boston. She will present new findings Monday showing the bapineuzumab did have a "significant difference" in altering biological signs of the disease, compared with the placebo.

Two large trials are being drawn up for pre-clinical patients. Another trial, funded partly by the government, is set to begin in mid-2013 on patients who carry a gene that ensures they'll develop Alzheimer's. If the therapy can prevent or delay the onset of the disease in them, the theory is that the therapy will work in people with other kinds of Alzheimer's.

"I don't think anyone was surprised the trials didn't work in people who had too much brain damage,'' Ryan says, "but you need to do these trials to study the data and learn how to move forward. We're doing that."